Very early in the morning of Tuesday Sept. 3rd amateur astronomer Bill Yeung imaged an object with fairly fast motion across the sky. This object, which is software designated as J002E3, was promptly placed on the Minor Planet Center's WWW NEO Confirmation Page.

J002E3 discovery images taken by Bill Yeung on September 3, 2002. Animation by Bob Denny

The next night Bill tried to re-observe it, but could not find it near the predicted position. At least one other observer reported the same result: It was not there. Maybe it was never there, just a false detection.
But on the second night, while Bill was weathered out in California, the LINEAR survey picked up an object with similar position and motion, which was placed on the NEOCP alongside Bill's discovery. Bill pointed out the similarities on the Minor Planet Mailing List (http://groups.yahoo.com/group/mpml/), and later the two discoveries were linked by MPC staff. J002E3, or 2E3 for short, was found, but it was almost immediately apparent that this object might be orbiting the Earth and not the sun. That tentative conclusion became firm as observations of this unusual object started to pour in over the next couple of days.
Over the weekend it was removed from the NEOCP with the terse remark, "J002E3 is not a minor planet," although this conclusion was perhaps somewhat premature.

Starting Monday morning my colleague Paul Chodas and I started gathering measurements of 2E3's position and computing orbits. In those early days, with barely a week of observations we could not say much about the object's past or future paths; however, it was obviously orbiting the Earth, with a period of around 42 days. It appeared that 2E3 had been captured from a very Earth-like heliocentric orbit in April of this year, and there was a good chance that it would leave the Earth's vicinity sometime in the middle of 2003. There was also some chance that it would impact the Earth or Moon

We speculated that this could be an Apollo Saturn V third stage, known as the SIV-B. These were the right brightness to match 2E3 and nothing else that bright has ever been sent beyond the Moon's orbit. The last five Apollo SIV-Bs (Apollos 13-17) were known to have impacted the Moon as part of the program's lunar seismology experiment, but mission controllers sent five earlier SIV-B stages (from Apollos 8-12) flying out of the Earth-Moon system.
Or at least that's what they had intended to do.
It worked for the SIV-Bs from Apollos 8-11, but for Apollo 12 the maneuver did not go according to plan. A glitch left the SIV-B on a distant orbit, very loosely bound to the Earth. This orbit was, coincidentally, rather similar to the one that 2E3 is in now.

There are several reasons that one would not expect to find natural objects on orbits like that of 2E3. First, objects with this kind of trajectory are rapidly swept up by colliding with the Earth and Moon, implying that an object cannot survive long in such an orbit, perhaps several thousand years at most. The Earth keeps its neighborhood very clean. Furthermore, how could it get on such an orbit?
One argument, based upon celestial mechanics, states that an object originating outside the Earth-Moon system cannot get onto such an orbit through simple planetary encounters. But how could an "asteroid" originate from the Earth or Moon? The possibility that an object this large was ejected from the Moon by a giant impact could not be ruled out, but if so there should be evidence for a large and very recent impact crater on the Moon. No candidate crater has been identified.

An animation by NEO JPL Program Office showing how J002E3 was captured into its chaotic orbit around the Earth, and how it will be leaving Earth orbit.

Since it was hard to explain how an object could naturally be on an orbit such as this, we wondered if the orbits of the five lost SIV-Bs could be linked to the orbit of 2E3. The answer was a resounding, "Maybe later, with more data," but as observational data continued to accumulate the motion of 2E3 became more tightly constrained.We were soon sure that it was indeed captured by the Earth in April 2002 and that it would escape back onto a heliocentric orbit in June 2003. We eventually were able to ascertain that it had escaped from Earth orbit in Feb. 1971! This ruled out all of the Apollo SIV-B stages except for Apollo 12. But that possibility required that the Apollo 12 SIV-B had remained in its loosely bound geocentric orbit for more than a year before "leaking" away from the Earth. That is an entirely plausible scenario, but far from conclusive.

While this was going on, Rob Whiteley and Carl Hergenrother of the Univ. of Arizona measured the rotation rate and color of 2E3. They found that it had a rather short rotation period (63.5 seconds) and that the colors were quite similar to the titanium oxide paint that was used on the Apollo rocket bodies. They pointed out that the color of J002E3 was not similar to other known asteroid classes. Later Rick Binzel and Andy Rivken of MIT took an infrared spectrum of 2E3, confirming that the object is a "dead ringer" for white paint.

Another clue is that 2E3 is not following a "ballistic" trajectory. From its motion, we are able to clearly see and measure the gentle push of solar radiation pressure on this object. Since radiation pressure is observable we can now rule out the possibility that 2E3 is an asteroid, but more compelling is the fact that the measured nongravitational acceleration is exactly what we would expect for an SIV-B stage.

At this time it is clear that 2E3 is a man-made object, and very likely the lost Apollo 12 SIV-B stage. But can that be confirmed? A loose-knit community of amateur astronomers continues to measure the position of 2E3 and pass the positions along to us. Richard Fredrick and Kyle Smalley of Powell Observatory in Kansas have been particularly diligent in tracking 2E3. As the observed arc lengthens we will be able to peer farther back into the history of this object. Presently we are able to predict the motion as far back as October 1970. That is two Earth orbits before it escaped in February 1971, but still around eight revolutions after the last confirmed position of the Apollo 12 SIV-B.
We hope that observers will continue to track this object and that before it fades from view next summer we will be able to confirm the identity of J002E3.